Image forming apparatus

ABSTRACT

According to an embodiment, an image forming apparatus has a fixing unit which heats an image formed on a recording medium at a fixing temperature, to fix the image on the recording medium. When a heating temperature of the fixing unit becomes a temperature higher than the fixing temperature, the image forming apparatus switches image forming, from image forming by a first mode using a discolorable coloring material, to image forming by a second mode using a non-discolorable coloring material.

CROSS-REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromthe prior Japanese Patent Application No. 2013-46574, filed on Mar. 8,2013, the entire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an image formingapparatus.

BACKGROUND

An image forming apparatus which forms an image with erasable coloringmaterial has already been put into practical use. As the erasablecoloring material, coloring material which is made transparent byheating is known. For example, an image forming apparatus can form anerasable full color image with erasable coloring materials of BK(black), C (cyan), M (magenta), Y (yellow).

The image forming apparatus forms an image of toner on a photoconductordrum with erasable coloring material, such as erasable toner. The imageforming apparatus primarily transfers the toner image from thephotoconductor drum to a transfer belt. The image forming apparatussecondarily transfers the toner image from the transfer belt to arecording medium, such as a sheet. The image forming apparatus fixes thetoner image transferred to the sheet by heating by a fixing unit. Thefixing unit is temperature controlled so that a heating temperaturebecomes a fixing temperature within the range from 150 degrees to 180degrees.

As described above, the heating temperature of the fixing unit iscontrolled to the fixing temperature within the range of 150 degrees to180 degrees, but the heating temperature of the fixing unit may exceedan upper limit temperature of the fixing temperature. For example, beingheated by the fixing unit at not less than 190 degrees, the erasablecoloring material is made transparent.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing an example of a schematic configuration of animage forming apparatus according to a first embodiment.

FIG. 2 is a view showing an example of a schematic configuration of animage forming apparatus according to a second embodiment.

FIG. 3 is a diagram showing an example of a heating temperature of thefixing device of the image forming apparatus according to the first andsecond embodiments.

FIG. 4 is a view showing an example of switching of the image forming bya print mode of the image forming apparatus according to the first andsecond embodiments.

FIG. 5A is a view showing an example of a display screen which thedisplay unit of the image forming apparatus according to the first andsecond embodiments displays for guiding switching from the image formingby a first print mode to the image forming by a second print mode.

FIG. 5B is a view showing an example of a display screen which thedisplay unit of the image forming apparatus according to the first andsecond embodiments displays for guiding switching from the image formingby the second print mode to the image forming by the first print mode.

FIG. 6 is a flowchart showing an example of execution control ofswitching of the image forming by the print mode of the image formingapparatus according to the first and second embodiments.

FIG. 7 is a view showing an example of a specific configuration of theimage forming apparatus according to the first and second embodiments.

FIG. 8 is a view showing an example of a specific configuration of theimage forming apparatus, when a manual feed tray for erasing operationis loaded on the image forming apparatus according to the first andsecond embodiments.

FIG. 9 is a diagram showing an example of a functional block of theimage forming apparatus according to the first and second embodiments.

FIG. 10 is a flowchart showing an example of an erasing operation of theimage forming apparatus according to the first and second embodiments.

FIG. 11 is a flowchart showing an example of a return processing from anerasing operation to an image forming operation of the image formingapparatus according to the first and second embodiments.

DETAILED DESCRIPTION

According to an embodiment, an image forming apparatus has an imageforming unit, a fixing unit, a temperature control unit, and anoperation control unit. The image forming unit executes any imageforming out of image forming to form an image on a recording medium by afirst mode using a discolorable coloring material which discolors byheating, and image forming to form an image on a recording medium by asecond mode using a non-discolorable coloring material. The fixing unitheats the image formed on the recording medium at a fixing temperaturelower than a heating temperature at which the discolorable coloringmaterial discolors, to fix the image on the recording medium. Thetemperature control unit controls a heating temperature of the fixingunit to the fixing temperature. The operation control unit selects theimage forming by the second mode, when the heating temperature of thefixing unit becomes a temperature higher than the fixing temperature.

Hereinafter, further embodiments will be described with reference to thedrawings. In the drawings, the same symbols represent the same orsimilar portions.

Embodiments will be described with reference to FIG. 1, FIG. 2, FIG. 7to FIG. 9. Image forming apparatuses 1 according to the embodimentsshown in FIG. 1, FIG. 2, FIG. 7 to FIG. 9 are MFPs (multi-functionperipherals). Hereinafter, each of the image forming apparatuses 1according to the embodiments is simply referred to as the MFP 1.

FIG. 1 is a view showing a main portion of the MFP 1 of a firstembodiment for easily comprehending monochrome image forming using amonochrome discolorable coloring material and monochrome image formingusing a monochrome non-discolorable coloring material in the MFP 1. FIG.2 is a view showing a main portion of the MFP 1 of a second embodimentfor easily comprehending color image forming using discolorable coloringmaterials of a plurality of colors, and color image forming usingnon-discolorable coloring materials of a plurality of colors.

FIG. 7 to FIG. 9 are views each showing an example of the MFP 1 forrealizing color image forming by means of toners that are discolorablecoloring materials of a plurality of colors, and color image forming bymeans of toners that are non-discolorable coloring materials of aplurality of colors.

The MFPs 1 shown in FIG. 1 and FIG. 2 are a little different in theappearance and internal configuration thereof from the MFPs 1 shown inFIG. 7, FIG. 8, but may be the same.

The MFP 1 shown in FIG. 1 has a plurality of housing units to housecoloring materials 51 a, 61 a, respectively. The housing units to housethe respective coloring materials 51 a, 61 a are arranged along a sheetconveying direction (in FIG. 1, in the left and right direction). TheMFP 1 shown in FIG. 1 has image forming stations 321 a, 322 a. The imageforming stations 321 a, 322 a are arranged at positions facing thehousing units to house coloring material 51 a, 61 a, respectively. Thecoloring material 51 a is a discolorable BK (black) toner. The coloringmaterial 61 a is a non-discolorable BK toner.

The MFP 1 shown in FIG. 2 has a plurality of housing units to housecoloring materials 51 a, 51 b, 51 c, 51 d, 61 a, 61 b, 61 c, 61 drespectively. The housing units to house the respective coloringmaterials 51 a-51 d, 61 a-61 d are arranged along a sheet conveyingdirection (in FIG. 2, in the left and right direction). The MFP 1 shownin FIG. 2 has a first to an eighth image forming stations 321 a, 321 b,321 c, 321 d, 322 a, 322 b, 322 c, 322 d. The first to eighth imageforming stations 321 a-321 d, 322 a-322 d are arranged at positionsfacing the housing units to house coloring material 51 a-51 d, 61 a-61d, respectively. The coloring materials 51 a-51 d are discolorable BK(black), C (cyan), M (magenta), Y (yellow) toners, respectively. Thecoloring materials 61 a-61 d are non-discolorable BK, C, M, K toners,respectively.

The above-described housing units to house the toners 51 a-51 d and thetoners 61 a-61 d supply the toners 51 a-51 d and the toners 61 a-61 d todeveloping units of the image forming stations 321 a-321 d, 322 a-322 d,respectively. The MFP 1 has a configuration to replenish a toner whenthe remaining amount of the toner housed in each housing unit runsshort. For example, each of the housing units is detachably provided inthe main body of the MFP 1 so that the housing unit can be exchanged toa new housing unit. Accordingly, the MFP 1 has a configuration which,when the remaining amount of a toner runs short, the housing unit tohouse the toner whose remaining amount runs short is exchanged to a newhousing unit by a user, and thus can replenish the toner. The shortageof the toner remaining amount is detected by a remaining amountdetecting unit 30 described later. Each of the MFPs 1 (hereinafter,simply stated as the MFP 1, for simplicity) shown in FIG. 1 and FIG. 2has a first sheet discharge tray T11 and a second sheet discharge trayT12. The first sheet discharge tray T11 and the second sheet dischargetray T12 are provided to protrude from the side face of the main body ofthe MFP 1.

On the other hand, the MFP 1 shown in FIG. 7 and FIG. 8 has housingunits to house the above-described respective coloring materials 51 a-51d, 61 a-61 d. The housing units to house the respective coloringmaterials 51 a-51 d are arranged along a moving direction of anintermediate transfer belt 33 described later (in FIG. 7 and FIG. 8, inthe left and right direction). The housing units to house the coloringmaterials 61 a-61 d are arranged at the back sides (in the drawings, atthe rear face side) of the housing units to house the coloring materials51 a-51 d, respectively. Accordingly, the housing units to house thecoloring materials 61 a-61 d are in the state hidden by the coloringmaterials 51 a-51 d, respectively. The MFP 1 shown in FIG. 7 and FIG. 8has the above-described first to eighth image forming stations 321 a-321d, 322 a-322 d. The first to fourth image forming stations 321 a-321 dare arranged at positions facing the housing units to house the coloringmaterial 51 a-51 d, respectively. The fifth to eighth image formingstations 322 a-322 d are arranged at positions facing the housing unitsto house the coloring material 61 a-61 d, respectively. Accordingly, thefifth to eighth image forming stations 322 a-322 d are in the statehidden by the first to fourth image forming stations 321 a-321 d,respectively. The MFP 1 shown in FIG. 7 and FIG. 8 has theabove-described first sheet discharge tray T11 and second sheetdischarge tray T12. The first sheet discharge tray T11 and the secondsheet discharge tray T12 are provided at the positions enclosed by themain body of the MFP 1, in FIG. 7 and FIG. 8.

For example, the MFP 1 shown in FIG. 7 and FIG. 8 has a moving mechanismto move the first to eighth image forming stations 321 a-321 d, 322a-322 d to the facing positions of the intermediate transfer belt 33,and the positions displaced from the facing positions. The movingmechanism moves the first image forming station (or the fifth imageforming station) to be used, out of the first image forming station 321a and the fifth image forming station 322 a, to the facing position ofthe intermediate transfer belt 33. The moving mechanism moves the fifthimage forming station (or the first image forming station) not to beused, out of the first image forming station 321 a and the fifth imageforming station 322 a, to the position displaced from the facingposition of the intermediate transfer belt 33. The fifth image formingstation (or the first image forming station) not to be used becomes in astandby state at the position displaced from the facing position.

Similarly as described above, the moving mechanism moves the secondimage forming station (or the sixth image forming station) to be used,out of the second image forming station 321 b and the sixth imageforming station 322 b, to the facing position of the intermediatetransfer belt 33. The moving mechanism moves the sixth image formingstation (or the second image forming station) not to be used, out of thesecond image forming station 321 b and the sixth image forming station322 b, to the position displaced from the facing position of theintermediate transfer belt 33. The sixth image forming station (or thesecond image forming station) not to be used becomes in a standby stateat the position displaced from the facing position.

Similarly as described above, the moving mechanism moves the third imageforming station (or the seventh image forming station) to be used, outof the third image forming station 321 c and the seventh image formingstation 322 c, to the facing position of the intermediate transfer belt33. The moving mechanism moves the seventh image forming station (or thethird image forming station) not to be used, out of the third imageforming station 321 c and the seventh image forming station 322 c, tothe position displaced from the facing position of the intermediatetransfer belt 33. The seventh image forming station (or the third imageforming station) not to be used becomes in a standby state at theposition displaced from the facing position.

Similarly as described above, the moving mechanism moves the fourthimage forming station (or the eighth image forming station) to be used,out of the fourth image forming station 321 d and the eighth imageforming station 322 d, to the facing position of the intermediatetransfer belt 33. The moving mechanism moves the eighth image formingstation (or the fourth image forming station) not to be used, out of thefourth image forming station 321 d and the eighth image forming station322 d, to the position displaced from the facing position of theintermediate transfer belt 33. The eighth image forming station (orfourth image forming station) not to be used becomes in a standby stateat the position displaced from the facing position.

The MFP 1 arranges the housing units of the coloring materials and theimage forming stations as shown in FIG. 7 and FIG. 8, and thereby theMFP can make the size of the MFP 1 in the width direction (in thedrawings, in the left and right direction) small. On the other hand, theMFP 1 arranges the housing units of the coloring materials and the imageforming stations as shown in FIG. 1 and FIG. 2, and thereby the MFP 1can make the size of the MFP 1 in the front-back direction (in thedrawings in the front and rear direction) small. The MFP 1 shown in FIG.7 and FIG. 8 can also be configured like the MFP 1 shown in FIG. 1. TheMFP 1 shown in FIG. 7 and FIG. 8 can also be configured like the MFP 1shown in FIG. 2.

For example, when the MFP 1 shown in FIG. 7 and FIG. 8 is configuredlike the MFP 1 shown in FIG. 1, in the MFP 1 shown in FIG. 7 and FIG. 8,the housing units to house the coloring materials 51 a, 61 a arearranged along the moving direction (in FIG. 7 and FIG. 8, in the leftand right direction) of the intermediate transfer belt, that is, theleft and right direction of the main body, and the image formingstations 321 a, 322 a are arranged at the positions facing the housingunits to house the coloring materials 51 a, 61 a, respectively.

When the MFP 1 shown in FIG. 7 and FIG. 8 is configured like the MFP 1shown in FIG. 2, in the MFP 1 shown in FIG. 7 and FIG. 8, the housingunits to house the coloring materials 51 a-51 d, 61 a-61 d are arrangedalong the moving direction (in FIG. 7 and FIG. 8, in the left and rightdirection) of the intermediate transfer belt, that is the left and rightdirection of the main body, and the first to eighth image formingstations 321 a-321 d, 322 a-322 d are arranged at the positions facingthe housing units to house the coloring materials 51 a-51 d, 61 a-61 d,respectively.

For example, the image forming station 321 a provided in the MFP 1 shownin FIG. 1 forms a BK monochrome image using the discolorable BK coloringmaterial 51 a. The image forming station 322 a provided in the MFP 1forms a BK monochrome image using the non-discolorable BK coloringmaterial 61 a. The MFP 1 has conveying units to convey a sheet on whichimages have been formed by the image forming stations 321 a, 322 a.

When the image forming stations 321 a, 322 a use an electrophotographicsystem as the image forming system, the MFP 1 has a fixing unit 35. Theabove-described conveying units convey the image formed sheet to thefixing unit 35. The fixing unit 35 heats the toner image formed on thesheet at a prescribed fixable temperature, to fix the image on thesheet.

The above-described image forming system is not limited to anelectrophotographic system. For example, when the image forming stations321 a, 322 a use an ink jet recording system as the image formingsystem, each of the image forming stations 321 a, 322 a forms an imageusing ink as the coloring material on the sheet conveyed by theconveying units.

Color of the monochrome image formed by each of the image formingstations 321 a, 322 a may be optional. The BK image which the imageforming station 321 a forms is formed using the BK coloring material 51a which can be discolored under a prescribe condition. The coloringmaterial 51 a is a BK discolorable toner, or a BK discolorable ink.

The BK image which the image forming station 322 a forms is formed usingthe BK coloring material 61 a which can not be discolored under aprescribe condition. The coloring material 61 a is a BK non-discolorabletoner, or a BK non-discolorable ink.

An example of the above-described prescribed condition is heat(temperature). When the discolorable toner 51 a is heated at aprescribed temperature higher than a heating temperature (fixingtemperature) of the fixing unit 35 at the time of fixing, the colorthereof is erased and discolored. For example, when the toner 51 a thatis a discolorable coloring material is heated at a prescribedtemperature (discoloring temperature) higher than the fixingtemperature, the color thereof changes to a color different from theoriginal color. The different color is a transparent color, for example.Accordingly, the fixing unit 35 heats an image formed using thediscolorable toner 51 a at the discoloring temperature, to discolor theimage. In addition, when the discoloring toner 51 a is heated at aprescribed temperature (erasing temperature) higher than theabove-described discoloring temperature, the color thereof changes fromthe original color to a transparent color with a permeability of 100%.In other words, when the discolorable toner 51 a is heated at theerasing temperature, the color thereof disappears. Hereinafter, it iscalled decoloring that a color disappears. Accordingly, the fixing unit35 heats an image formed using the discoloring toner 51 a at the erasingtemperature, to erase the image. The discolorable ink 51 a is decoloredor discolored at a heating temperature lower than the discolorable toner51 a, depending on the composition of dyes contained in the ink. Anotherexample of the above-described prescribed condition is light(ultraviolet rays and so on). The discolorable ink 51 a is decolored ordiscolored with the radiation of ultraviolet rays and so on, dependingon the composition of dyes contained in the ink.

For example, the first to fourth image forming stations 321 a-321 dprovided in the MFP 1 shown in FIG. 2 and FIG. 7 form monochrome imagesof BK, C, M, Y using the discolorable coloring materials 51 a-51 d ofBK, C, M, Y, respectively. The MFP 1 has conveying units to convey asheet on which images have been formed by the image forming stations 321a-321 d.

When the image forming stations 321 a-321 d use an electrophotographicsystem as the image forming system, the MFP 1 has the fixing unit 35.The above-described conveying units convey the sheet on which tonerimages of BK, C, M, Y have been formed to the fixing unit 35. The fixingunit 35 heats the toner images formed on the sheet at a prescribedfixing temperature, to fix the images on the sheet.

Also the above-described image forming system of the MFP 1 shown in FIG.2 and FIG. 7 is not limited to an electrophotographic system. Forexample, when the image forming stations 321 a-321 d use an ink jetrecording system as the image forming system, each of the image formingstations 321 a-321 d forms an image using ink as the coloring materialon the sheet conveyed by the conveying units.

Colors of the monochrome images formed by the first to fourth imageforming stations 321 a-321 d may be optional. The colors of theabove-described monochrome images can variously be combined depending onthe characteristics of toners to be used and colors of inks to be used.

The images of the four colors of BK, C, M, Y to be formed by the firstto fourth image forming stations 321 a-321 d are formed using thecoloring materials 51 a-51 d of BK, C, M, Y which can be discoloredunder prescribed conditions, respectively. The coloring material 51 a isthe BK discolorable toner, or the BK discolorable ink, as describeabove. The coloring material 51 b is the C discolorable toner, or the Cdiscolorable ink, as describe above. The coloring material 51 c is the Mdiscolorable toner, or the M discolorable ink, as describe above. Thecoloring material 51 d is the Y discolorable toner, or the Ydiscolorable ink, as describe above.

The images of the four colors of BK, C, M, Y to be formed by the fifthto eighth image forming stations 322 a-322 d provided in the MFP 1 shownin FIG. 2 and FIG. 7 are formed using the coloring materials 61 a-61 dof BK, C, M, Y which can not be discolored under prescribed conditions,respectively. The coloring material 61 a is the BK non-discolorabletoner, or the BK non-discolorable ink. The coloring material 61 b is theC non-discolorable toner, or the C non-discolorable ink. The coloringmaterial 61 c is the M non-discolorable toner, or the M non-discolorableink. The coloring material 61 d is the Y non-discolorable toner, or theY non-discolorable ink.

An example of the above-described prescribed condition is heat(temperature), as described above. When the discolorable toners 51 a-51d are heated at a prescribed temperature higher than a heatingtemperature (fixing temperature) of the fixing unit 35 at the time offixing, the colors thereof are erased and discolored. For example, whenthe toners 51 a-51 d that are discolorable coloring materials are heatedat a prescribed temperature (discolorable temperature) higher thanfixing temperature, the colors thereof change to colors different fromthe original colors. The different colors are a transparent color, forexample. Accordingly, the fixing unit 35 heats images formed using thediscolorable toners 51 a-51 d at the discoloring temperature, todiscolor the images. In addition, when the discoloring toners 51 a-51 dare heated at a prescribed temperature (erasing temperature) higher thanthe above-described discoloring temperature, the colors thereof changefrom the original colors to a transparent color with a permeability of100%. In other words, when the discolorable toners 51 a-51 d are heatedat the erasing temperature, the colors thereof disappear. Hereinafter,it is called decoloring that colors disappear. Accordingly, the fixingunit 35 heats the images formed using the discoloring toners 51 a-51 dat the erasing temperature, to erase the images. The discolorable inks51 a-51 d are decolored or discolored at a heating temperature lowerthan the discolorable toners 51 a-51 d, depending on the compositions ofdyes contained in the inks. Another example of the above-describedprescribed condition is light (ultraviolet rays and so on). Thediscolorable inks 51 a-51 d are decolored or discolored with theradiation of ultraviolet rays and so on, depending on the compositionsof dyes contained in the inks.

A specific example of the discolorable toners 51 a-51 d which the MFP 1uses, and the principle of discoloring and decoloring the discolorabletoners 51 a-51 d will be further described.

When the discolorable toners 51 a-51 d which the MFP 1 uses are heatedto a discoloring temperature, discoloring thereof is started. When thediscolorable toners 51 a-51 d are further heated to an erasingtemperature, the colors thereof become a transparent color with apermeability of 100%, and are decolored. Specifically, each of thediscolorable toners 51 a-51 d contains a binder resin and a coloringmatter. The binder resin is the same as in the conventional andwell-known toner (non-discolorable toner). The discolorable toners 51a-51 d are characterized in coloring matters. The coloring mattercontains a coloring compound, a color developer, a discoloringtemperature control agent (temperature control agent). The coloringcompound is a color developing agent, and a leuco dye is used, forexample. Phenols are used as the color developer, for example. Substancewhich becomes compatible with the coloring compound when heated and doesnot have affinity with the color developer is used as the discoloringtemperature control agent. The coloring compound generates a color by amutual action with the color developer, to cause the discolorable tonerto develop a prescribed color. When the discolorable toner is heated tonot less than the discoloring temperature, the mutual reaction of thecoloring compound with the color developer is weakened, and thereby thediscolorable toner begins to discolor to a transparent color. When thediscolorable toner is further heated to not less than the erasingtemperature, the mutual reaction of the coloring compound with the colordeveloper is broken, and thereby the discolorable toner is decolored.The above-described discoloring temperature and erasing temperature canbe controlled by arbitrarily combining the discoloring temperaturecontrol agents.

Hereinafter, a specific configuration of the MFP 1 will be describedwith reference to FIG. 7 to FIG. 9. The MFP 1 will be described as onewhich forms an image by means of an electrophotographic system usingtoners as the coloring materials 51 a-51 d, 61 a-61 d. As shown in FIG.7 to FIG. 9, the MFP 1 has at least an image forming unit 3, a fixingunit 35, an image reading unit 5, an operation panel 9, and an operationcontrol unit 7. The operation control unit 7 performs signal processingand operation control as described later. The operation control unit 7is composed of a circuit board. The operation panel 9 has a display unit9 a as described later. The operation panel 9 is arranged at aprescribed position of the MFP 1.

The image forming unit 3 forms a visible image (toner image)corresponding to image data on a recording medium, such as a paper or aresin sheet. The image data may be data generated by the image readingunit 5, or may be data obtained from the outside, for example. The imagedata obtained from the outside may be data which a portable storagemedium such as a semiconductor memory supplies to the MFP 1, and may bedata which a supply source such as a PC (Personal Computer) on a networksupplies to the MFP 1 through an I/F (Interface) 71 as shown in FIG. 9.

The image forming unit 3 further has the remaining amount detecting unit30 shown in FIG. 9. The remaining amount detecting unit 30 detectsshortage of remaining amounts of the toners 51 a-51 d, 61 a-61 d used inthe image forming stations 321 a-321 d, 322 a-322 d, respectively.Specifically, the remaining amount detecting unit 30 detects that theremaining amounts of the toners 51 a-51 d, 61 a-61 d become less thanprescribed values, respectively. The image reading unit 5 acquirescharacters or an image of a document that is a reading target asbrightness of light, and generates image data corresponding to thebrightness.

The image reading unit 5 includes at least a document table 5 a, anillumination device, and an image sensor. The document table 5 asupports a document that is the reading target. The document table 5 ais composed of a transparent member, such as glass. The illuminationdevice emits light toward the document supported by the document table 5a. The image sensor converts reflected light (image information) fromthe document into an image signal. The image sensor is a CCD (ChargeCoupled Device) sensor or a CMOS (Complementary metal-oxideSemiconductor) sensor, for example.

The above-described operation control unit 7 processes the image signalgenerated by the image reading unit 5, to convert the above-describedimage signal into image data suitable for image forming by the imageforming unit 3. Specifically, the operation control unit 7 performs, forimage forming, prescribed processings, such as character specification,outline correction, color tone correction (color conversion, RGB→CMY,concentration), half tone (gradation) processing, and γ characteristic(input concentration value to output concentration) processing to theimage signal from the image sensor. The image signal and the image dataare stored in a storage device not shown, such as a HDD (Hard DiskDrive), or a semiconductor memory and so on which is removable from theMFP 1.

The MFP 1 shown in FIG. 1 has an exposure unit 31, and theabove-described image forming stations 321 a, 322 a, as the imageforming unit 3. The MFP 1 shown in FIG. 2, FIG. 7 and FIG. 8 has theexposure unit 31, and the above-described image forming stations 321a-321 d, 322 a-322 d.

The MFP 1 shown in FIG. 7 and FIG. 8 further has primary transfer unitsdescribed later the intermediate transfer belt 33, a secondary transferunit 34, the above-described fixing unit 35, waste toner collectingmechanisms 36, an intermediate transfer belt cleaner 37 and a wastetoner recovery device 38 and so on. The above-described fixing unit 35functions also as a unit to erase an image and discolor an image.

The image forming unit 3 of the MFP 1 further has a sheet feeding unit,an aligning mechanism 45 and an ADU (Automatically Duplex Unit) 40. Thesheet feeding unit includes at least one sheet cassette 41, a manualfeed tray, and a second manual feed tray 146. The sheet cassette 41houses a sheet for image forming. The sheet cassette 41 is detachablyloaded in a cassette loading unit provided at the lower portion of themain body of the MFP 1. The image forming unit 3 further has a sheetfeeding mechanism 42, a separation mechanism 43, and a conveyingmechanism 44, as conveying units provided for each cassette 41.

The manual feed tray 46 holds a sheet for image forming. The manual feedtray 46 is detachably loaded on a first tray loading unit provided atthe lower portion of the side face of the main body of the MFP 1.Specifically, the first tray loading unit includes a fulcrum 46 a. Themanual feed tray 46 is detachably loaded on the fulcrum 46 a. The manualfeed tray 46 loaded on the fulcrum 46 a is supported rotatably aroundthe fulcrum 46 a in the direction of an arrow A, and thereby can beopened and closed against the side face of the main body of the MFP 1.The manual feed tray 46 substantially closely contacts the side face ofthe main body of the MFP 1 in the closed state. The manual feed tray 46separates from the side face of the main body of the MFP 1 in the openstate, and becomes holdable a sheet. Accordingly, when using the manualfeed tray 46, a user can open the manual feed tray 46 against the sideface of the main body of the MFP 1. When not using the manual feed tray46, the user can close the manual feed tray 46 against the side face ofthe main body of the MFP 1.

The image forming unit 3 has a sheet feeding mechanism 47, a separationmechanism 48, and a timing matching mechanism 49, as conveying units forthe manual feed tray 46. The fulcrum 46 a of the first tray loadingunit, the sheet feeding mechanism 47, the separation mechanism 48 andthe timing matching mechanism 49 are arranged at the front stage of thealigning mechanism 45.

The sheet feeding mechanism 47 takes out a sheet from the manual feedtray 46. The separation mechanism 48 separates the sheets taken out fromthe manual feed tray 46 one by one. The timing matching mechanism 49conveys the sheet which has been separated one by one to the aligningmechanism 45 in matching with the operation of the image forming unit 3.

The second manual feed tray 146 holds a sheet for erasing an imageformed on a sheet and for discoloring the image. The second manual feedtray 146 is loaded on a second tray loading unit provided at the upperportion of the side face of the main body of the MFP 1. Specifically,the second tray loading unit includes a fulcrum 146 a. The second manualfeed tray 146 is detachably loaded on the fulcrum 146 a. The secondmanual feed tray 146 loaded on the fulcrum 146 a is supported rotatablyaround the fulcrum 146 a in the direction of an arrow A, and thereby canbe opened and closed against the side face of the main body of the MFP1. The second manual feed tray 146 substantially closely contacts theside face of the main body of the MFP 1 in the closed state. The secondmanual feed tray 146 separates from the side face of the main body ofthe MFP 1 in the open state, and becomes holdable a sheet. Accordingly,when using the second manual feed tray 146, a user can open the secondmanual feed tray 146 against the side face of the main body of the MFP1. When not using the second manual feed tray 146, the user can closethe second manual feed tray 146 against the side face of the main bodyof the MFP 1.

The image forming unit 3 has a sheet feeding mechanism 147, a separationmechanism 148, and a timing matching mechanism 149 as conveying unitsfor the second manual feed tray 146. A fulcrum 146 a of the second trayloading unit, the sheet feeding mechanism 147, the separation mechanism148 and the timing matching mechanism 149 are arranged at the rear stageof the aligning mechanism 45, and between the transfer position and thefixing unit 35. The above-described transfer position is a positionwhere the intermediate transfer belt 33 and the secondary transfer unit34 contact.

The sheet feeding mechanism 147 takes out a sheet from the second manualfeed tray 146. The separation mechanism 148 separates the sheets takenout from the second manual feed tray 146 one by one. The timing matchingmechanism 149 conveys the sheet which has been separated one by one tofixing unit 35 in matching with the operation of the fixing unit 35.

The exposure unit 31 of the MFP 1 shown in FIG. 1 converts the imagedata outputted from an image processing unit 73 of the operation controlunit 7 into strength and weakness of laser light. The exposure unit 31irradiates a photoconductor drum of the image forming station 321 a orthe image forming station 322 a with the laser light converted from theBK image data. The exposure unit 31 forms an electrostatic latent imageon each of the photoconductor drums of the image forming stations 321 a,322 a by the laser light irradiation.

The image forming station 321 a has the above-described photoconductordrum that is an image carrier, a developing unit and a primary transferunit. The photoconductor drum of the image forming station 321 a is forBK image forming. The photoconductor drum of the image forming station321 a generates an electrostatic latent image corresponding to laserlight for forming a BK image which is irradiated by the exposure unit31. The developing unit of the image forming station 321 a supplies thediscolorable BK toner 51 a to the photoconductor drum for BK imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 321 a develops theabove-described electrostatic latent image, to form an image of thediscolorable BK toner 51 a on the photoconductor drum for BK imageforming. The primary transfer unit of the image forming station 321 atransfers the image of the discolorable BK toner 51 a which has beenformed on the photoconductor drum for BK image forming to theintermediate transfer belt 33.

The intermediate transfer belt 33 primarily holds the image formed bythe image forming station of the image forming unit 3. Specifically, theintermediate transfer belt 33 holds the discolorable toner image formedby the image forming station 321 a, and conveys the image to theabove-described transfer position.

The image forming station 322 a forms an image using non-discolorabletoner that is the coloring material 61 a. In other words, the imageforming station 322 a forms an image of the non-discolorable BK toner 61a.

The image forming station 322 a, similarly as the above-described imageforming station 321 a, has the above-described photoconductor drum thatis an image carrier, a developing unit and a primary transfer unit. Thephotoconductor drum of the image forming station 322 a is for BK imageforming. The photoconductor drum of the image forming station 322 agenerates an electrostatic latent image corresponding to laser light forforming a BK image which is irradiated by the exposure unit 31. Thedeveloping unit of the image forming station 322 a supplies thenon-discolorable BK toner 61 a to the photoconductor drum for BK imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 322 a develops theabove-described electrostatic latent image, to form an image of thenon-discolorable BK toner 61 a on the photoconductor drum for BK imageforming. The primary transfer unit of the image forming station 322 atransfers the image of the non-discolorable BK toner 61 a which has beenformed on the photoconductor drum for BK image forming to theintermediate transfer belt 33.

The intermediate transfer belt 33 holds the non-discolorable toner imageformed by the image forming station 322 a, and conveys the image to theabove-described transfer position.

The secondary transfer unit 34 transfers the above-described toner imageconveyed by the intermediate transfer belt 33 from the intermediatetransfer belt 33 to the sheet at the above-described transfer position.

The fixing unit 35 fixes the above-described toner image transferredfrom the intermediate transfer belt 33 to the sheet by the secondarytransfer unit 34 on the sheet.

Toner (primary transfer remaining toner) remaining on the photoconductordrum of each of the image forming stations 321 a, 322 a without beingtransferred from the photoconductor drum to the intermediate transferbelt 33 is removed by a cleaner not shown. The waste toner collectingmechanism 36 collects the primary transfer remaining toner removed bythe above-described cleaner, so that the waste toner recovery device 38described later recovers the primary transfer remaining toner. The wastetoner collecting mechanism 36 collects the above-described primarytransfer remaining toner, in the vicinity of the above-described primarytransfer unit of each of the image forming stations 321 a, 322 a.

After the secondary transfer by the above-described secondary transferunit 34, toner which has not been transferred to the sheet remains onthe intermediate transfer belt 33 (secondary transfer remaining toner).The intermediate transfer belt cleaner 37 removes and collects thesecondary transfer remaining toner from the intermediate transfer belt33, so that the waste toner recovery device 38 described later recoversthe secondary transfer remaining toner. The intermediate transfer beltcleaner 37 collects the secondary transfer remaining toner in thevicinity of the secondary transfer unit 34.

The waste toner recovery device 38 recovers the primary transferremaining toners collected by the waste toner collecting mechanisms 36,and the secondary transfer remaining toner collected by the intermediatetransfer belt cleaner 37.

The sheet feeding mechanism 42 takes out a sheet from the sheet cassette41 in response to the image forming operation in the image formingstations 321 a, 322 a. The separation mechanism 43 separates the sheetstaken out by the sheet feeding mechanism 42, one by one. The conveyingmechanism 44 conveys the sheet separated one by one by the separationmechanism 43 to the aligning mechanism 45. The aligning mechanism 45conveys the sheet to the above-described transfer position in matchingwith the timing of the image forming operation in the image formingstations 321 a, 322 a. Accordingly, the sheet taken out from the sheetcassette 41 by the sheet feeding mechanism 42 and separated one by oneby the separation mechanism 43 moves to the above-described transferposition through the conveying mechanism 44 and the aligning mechanism45.

When the MFP 1 forms an image on a sheet, the fixing unit 35 heats andpressurizes the sheet and the toner image electrostatically attached tothe sheet at a fixing temperature, to fix the toner image to the sheet.Specifically, the toner electrostatically transferred to the sheet bythe secondary transfer unit 34 is heated by the fixing unit 35 at thefixing temperature, and is melt. In the toner, the coloring compoundgenerates a color by the action with the color developer, and therebythe toner develops a prescribed color. While keeping the state todevelop the prescribed color, the above-described melted toner ispressurized by the fixing unit 35, and thereby the toner image is fixedto the sheet.

The MFP 1 has a discharge unit and a discharge roller not shown. Thedischarge unit is provided in a space portion between the reading unit 5and the image forming unit 3. The discharge unit holds a sheet to bedischarged outside the MFP 1. The discharge roller is provided at theback stage of the fixing unit 35. The discharge roller discharges thesheet on which the toner image has been fixed to the above-describeddischarge unit, in cooperation with the fixing unit 35. In the case offorming images on both faces of a sheet, the above-described dischargeroller inversely rotates, to send the sheet which has been dischargedpartway in the discharge unit into the ADU 40.

The exposure unit 31 of the image forming unit 3 converts the image dataoutputted by the image processing unit 73 of the operation control unit7 into strength and weakness of laser light, as described above. Theexposure unit 31 irradiates the photoconductor drums of the first tofourth image forming station 321 a-321 d or the fifth to eighth imageforming station 322 a-322 d with the laser lights converted from theimage data of the respective colors of BK, C, M, Y. Or the exposure unit31 irradiates the photoconductor drum of the first image forming station321 a or the fifth image forming station 322 a, the photoconductor drumof the second image forming station 321 b or the sixth image formingstation 322 b, the photoconductor drum of the third image formingstation 321 c or the seventh image forming station 322 c, and thephotoconductor drum of the fourth image forming station 321 d or theeighth image forming station 322 d, with the laser light converted fromthe image data.

The exposure unit 31 forms an electrostatic latent image on each of thephotoconductor drums of the first to eighth image forming stations 321a-321 d, 322 a-322 d by the laser light irradiation.

For example, when the MFP 1 forms a full color image using thediscolorable toners 51 a-51 d, the exposure unit forms an electrostaticlatent image on each of the photoconductor drums of the first to fourthimage forming stations 321 a-321 d by the laser light irradiation. Theimage forming stations 321 a-321 d develop the above-describedelectrostatic latent images using the discolorable toners 51 a-51 d ofcolors of BK, C, M, Y, to form the images of the discolorable toners 51a-51 d of the colors of BK, C, M, Y on the photoconductor drums, as thevisualized images, respectively.

Each of the first to fourth image forming stations 321 a-321 d has theabove-described photoconductor drum that is an image carrier, thedeveloping unit and the primary transfer unit. The photoconductor drumof the image forming station 321 a is for BK image forming. Thephotoconductor drum of the image forming station 321 a generates anelectrostatic latent image corresponding to the laser light for forminga BK image which is irradiated by the exposure unit 31. The developingunit of the image forming station 321 a supplies the discolorable BKtoner 51 a to the photoconductor drum for BK image forming, to developthe above-described electrostatic latent image. The developing unit ofthe image forming station 321 a develops the above-describedelectrostatic latent image, to form an image of the discolorable BKtoner 51 a on the photoconductor drum for BK image forming. The primarytransfer unit of the image forming station 321 a transfers the image ofthe discolorable BK toner 51 a which has been formed on thephotoconductor drum for BK image forming to the intermediate transferbelt 33.

The photoconductor drum of the image forming station 321 b is for Cimage forming. The photoconductor drum of the image forming station 321b generates an electrostatic latent image corresponding to the laserlight for forming a C image which is irradiated by the exposure unit 31.The developing unit of the image forming station 321 b supplies thediscolorable C toner 51 b to the photoconductor drum for C imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 321 b develops theabove-described electrostatic latent image, to form an image of thediscolorable C toner 51 b on the photoconductor drum for C imageforming. The primary transfer unit of the image forming station 321 btransfers the image of the discolorable C toner 51 b which has beenformed on the photoconductor drum for C image forming to theintermediate transfer belt 33.

The photoconductor drum of the image forming station 321 c is for Mimage forming. The photoconductor drum of the image forming station 321c generates an electrostatic latent image corresponding to the laserlight for forming an M image which is irradiated by the exposure unit31. The developing unit of the image forming station 321 c supplies thediscolorable M toner 51 c to the photoconductor drum for M imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 321 c develops theabove-described electrostatic latent image, to form an image of thediscolorable M toner 51 c on the photoconductor drum for M imageforming. The primary transfer unit of the image forming station 321 ctransfers the image of the discolorable M toner 51 c which has beenformed on the photoconductor drum for M image forming to theintermediate transfer belt 33.

The photoconductor drum of the image forming station 321 d is for Yimage forming. The photoconductor drum of the image forming station 321d generates an electrostatic latent image corresponding to the laserlight for forming a Y image which is irradiated by the exposure unit 31.The developing unit of the image forming station 321 d supplies thediscolorable Y toner 51 d to the photoconductor drum for Y imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 321 d develops theabove-described electrostatic latent image, to form an image of thediscolorable Y toner 51 d on the photoconductor drum for Y imageforming. The primary transfer unit of the image forming station 321 dtransfers the image of the discolorable Y toner 51 d which has beenformed on the photoconductor drum for Y image forming to theintermediate transfer belt 33.

In the case of forming a full color image, images of the above-describeddiscolorable toners 51 a-51 d of the four colors are superposed andtransferred to the intermediate transfer belt 33. The arrangementposition of the image forming stations 321 a-321 d, in other words, anorder by which the images of the discolorable toners 51 a-51 d areformed on the intermediate transfer belt 33 is determined in accordancewith the image forming process and the characteristics of the toners.

The intermediate transfer belt 33 holds the images of the discolorabletoners formed by the first to fourth image forming stations 321 a-321 d,and transfers the images to the above-described transfer position.

When the MFP 1 forms an image using the non-discolorable toners 61 a-61d, the exposure unit 31 forms an electrostatic latent image on each ofthe photoconductor drums of the image forming stations 322 a-322 d bythe above-described laser light irradiation. The image forming stations322 a-322 d develop the above-described electrostatic latent imagesusing the non-discolorable toners 61 a-61 d of colors of BK, C, M, Y, toform the images of the non-discolorable toners 61 a-61 d of the colorsof BK, C, M, Y on the photoconductor drums, as the visualized images,respectively.

Each of the fifth to eighth image forming stations 322 a-322 d has theabove-described photoconductor drum that is an image carrier, thedeveloping unit and the primary transfer unit, similarly as theabove-described first to fourth image forming stations 321 a-321 d.

The photoconductor drum of the image forming station 322 a is for BKimage forming. The photoconductor drum of the image forming station 322a generates an electrostatic latent image corresponding to the laserlight for forming a BK image which is irradiated by the exposure unit31. The developing unit of the image forming station 322 a supplies thenon-discolorable BK toner 61 a to the photoconductor drum for BK imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 322 a develops theabove-described electrostatic latent image, to form an image of thenon-discolorable BK toner 61 a on the photoconductor drum for BK imageforming. The primary transfer unit of the image forming station 322 atransfers the image of the non-discolorable toner 61 a which has beenformed on the photoconductor drum for BK image forming to theintermediate transfer belt 33.

The photoconductor drum of the image forming station 322 b is for Cimage forming. The photoconductor drum of the image forming station 322b generates an electrostatic latent image corresponding to the laserlight for forming a C image which is irradiated by the exposure unit 31.The developing unit of the image forming station 322 b supplies thenon-discolorable C toner 61 b to the photoconductor drum for C imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 322 b develops theabove-described electrostatic latent image, to form an image of thenon-discolorable toner 61 b on the photoconductor drum for C imageforming. The primary transfer unit of the image forming station 322 btransfers the image of the non-discolorable toner 61 b which has beenformed on the photoconductor drum for C image forming to theintermediate transfer belt 33.

The photoconductor drum of the image forming station 322 c is for Mimage forming. The photoconductor drum of the image forming station 322c generates an electrostatic latent image corresponding to the laserlight for forming an M image which is irradiated by the exposure unit31. The developing unit of the image forming station 322 c supplies thenon-discolorable M toner 61 c to the photoconductor drum for M imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 322 c develops theabove-described electrostatic latent image, to form an image of thenon-discolorable M toner 61 c on the photoconductor drum for M imageforming. The primary transfer unit of the image forming station 322 ctransfers the image of the non-discolorable toner 61 c which has beenformed on the photoconductor drum for M image forming to theintermediate transfer belt 33.

The photoconductor drum of the image forming station 322 d is for Yimage forming. The photoconductor drum of the image forming station 322d generates an electrostatic latent image corresponding to the laserlight for forming a Y image which is irradiated by the exposure unit 31.The developing unit of the image forming station 322 d supplies thenon-discolorable Y toner 61 d to the photoconductor drum for Y imageforming, to develop the above-described electrostatic latent image. Thedeveloping unit of the image forming station 322 d develops theabove-described electrostatic latent image, to form an image of thenon-discolorable toner 61 d on the photoconductor drum for Y imageforming. The primary transfer unit of the image forming station 322 dtransfers the image of the non-discolorable toner 61 d which has beenformed on the photoconductor drum for Y image forming to theintermediate transfer belt 33. In the case of forming a full colorimage, images of the above-described four non-discolorable toners 61a-61 d of the four colors are superposed and transferred to theintermediate transfer belt 33. The arrangement position of the fifth toeighth image forming stations 322 a-322 d, in other words, an order bywhich the images of the non-discolorable toners 61 a-61 d are formed onthe intermediate transfer belt 33 is determined in accordance with theimage forming process and the characteristics of the toners.

The intermediate transfer belt 33 holds the images of thenon-discolorable toners formed by the fifth to eighth image formingstations, and transfers the images to the above-described transferposition.

The above-described secondary transfer unit 34 transfers theabove-described toner image conveyed by the intermediate transfer belt33 from the intermediate transfer belt 33 to the sheet at theabove-described transfer position.

The fixing unit 35 fixes the above-described toner image transferredfrom the intermediate transfer belt 33 by the secondary transfer unit 34to the sheet.

The toner (primary transfer remaining toner) remaining on thephotoconductor drum of each of the first to eighth image formingstations without being transferred from the photoconductor drum to theintermediate transfer belt 33 is removed by a cleaner not shown. Thewaste toner collecting mechanism 36 collects the primary transferremaining toner removed by the above-described cleaner, so that thewaste toner recovery device 38 described later recovers the primarytransfer remaining toner. The waste toner collecting mechanism 36collects the above-described primary transfer remaining toner, in thevicinity of each of the above-described primary transfer units of theimage forming stations.

After the secondary transfer by the above-described secondary transferunit 34, toner which has not been transferred to the sheet remains onthe intermediate transfer belt 33 (secondary transfer remaining toner).The intermediate transfer belt cleaner 37 removes and collects thesecondary transfer remaining toner from the intermediate transfer belt33, so that the waste toner recovery device 38 described later recoversthe secondary transfer remaining toner. The intermediate transfer beltcleaner 37 collects the secondary transfer remaining toner in thevicinity of the secondary transfer unit 34.

The waste toner recovery device 38 recovers the primary transferremaining toners collected by the waste toner collecting mechanisms 36,and the secondary transfer remaining toner collected by the intermediatetransfer belt cleaner 37.

The sheet feeding mechanism 42 takes out the sheet from the sheetcassette 41 in response to the image forming operation in the first toeighth image forming stations. The separation mechanism 43 separates thesheets taken out by the sheet feeding mechanism 42, one by one. Theconveying mechanism 44 conveys the sheet separated one by one by theseparation mechanism 43 to the aligning mechanism 45. The aligningmechanism 45 conveys the sheet to the above-described transfer positionin matching with the timing of the image forming operation in the firstto eighth image forming stations. Accordingly, the sheet taken out fromthe sheet cassette 41 by the sheet feeding mechanism 42 and separatedone by one by the separation mechanism 43 moves to the above-describedtransfer position through the conveying mechanism 44 and the aligningmechanism 45.

When the MFP 1 forms an image on a sheet, the fixing unit 35 heats andpressurizes the sheet and the toner image electrostatically attached tothe sheet at a fixing temperature, to fix the toner image to the sheet.Specifically, the toner electrostatically transferred to the sheet bythe secondary transfer unit 34 is heated by the fixing unit 35 at thefixing temperature, and is melt. In the toner, the coloring compoundgenerates a color by the action with the color developer, and therebythe toner develops a prescribed color. While keeping the state todevelop the prescribed color, the above-described melted toner ispressurized by the fixing unit 35, and thereby the toner image is fixedto the sheet.

The MFP 1 has a discharge unit and a discharge roller not shown. Thedischarge unit is provided in a space portion between the reading unit 5and the image forming unit 3. The discharge unit holds a sheetdischarged outside the MFP 1. The discharge roller is provided at theback stage of the fixing unit 35. The discharge roller discharges thesheet on which the toner image has been fixed to the above-describeddischarge unit, in cooperation with the fixing unit 35. In the case offorming images on both faces of a sheet, the above-described dischargeroller inversely rotates, to send the sheet which has been dischargedpartway in the discharge unit into the ADU 40. The ADU 40 conveys thesheet which has been sent therein by the discharge roller to thealigning mechanism 45 again. The sheet is conveyed to the aligningmechanism 45 in the state in which the front and back of the sheet arereversed, so that a toner image is transferred to a second face (a rearface, for example) that becomes a back face of a first face (a frontface, for example) on which the toner image has been fixed.

The ADU 40 is supported rotatably around a fulcrum 40 a in the directionof an arrow A, as shown in FIG. 8, and thereby can be opened and closedagainst the side face of the main body of the MFP 1. The ADU 40substantially closely contacts the side face of the main body of the MFP1 in the closed state as shown in FIG. 7, so as to cover the fulcrum 146a of the second tray loading unit and the second manual feed tray 146loaded on the fulcrum 146 a. The ADU 40 becomes usable in the closedstate.

The ADU 40 separates from the side face of the main body of the MFP 1 inthe open state, so that the fulcrum 146 a of the second tray loadingunit and the second manual feed tray 146 loaded on the fulcrum 146 a areexposed, as shown in FIG. 8. For example, when sheet jam occurs in theMFP 1, a user can open the ADU 40 against the side face of the main bodyof the MFP 1, so as to remove the sheet from the MFP 1.

When the ADU 40 is in the closed state (when the ADU 40 is used), sincethe fulcrum 146 a of the second tray loading unit is covered with theADU 40, a user can not load the second tray 146 on the fulcrum 146 a,and can not unload it from the fulcrum 146 a. In addition, when the ADU40 is in the closed state, since the second manual feed try 146 loadedon the fulcrum 146 a is covered with the ADU 40, a user can not alsoopen the second manual feed tray 146.

On the other hand, when the ADU is in the open state (when the ADU 40 isnot used), since the fulcrum 146 a of the second tray loading unit isexposed, a user can load the second manual feed tray 146 on the fulcrum146 a, and can unload it from the fulcrum 146 a. In addition, when theADU 40 is in the open state, since the second manual feed tray 146loaded on the fulcrum 146 a is exposed, a user can also open the secondmanual feed tray 146.

In other words, the second manual feed tray 146 becomes unusable whenthe ADU 40 is in the closed state, and becomes usable when the ADU 40 isin the open state. It is not necessary that the second manual feed tray146 is usually loaded on the fulcrum 146 a of the second tray loadingunit. A user may load the second manual feed tray 146 on the fulcrum 146a, only when erasing the image formed on the sheet and discoloring theimage.

The second manual feed tray 146 has the same structure as the manualfeed tray 46. Accordingly, as shown in FIG. 8, a user can unload themanual feed tray 46 from the fulcrum 46 a in the direction of an arrowB, and can load the unloaded manual feed tray 46 on the fulcrum 146 a ofthe second tray loading unit, in the direction of an arrow C. The manualfeed tray 46 is made usable as the second manual feed tray 146, andthereby the component cost in the MFP 1 can be reduced.

A control configuration of the MFP 1 will be described with reference toFIG. 9. FIG. 9 is a block diagram showing a control configuration of theMFP 1 according to the first embodiment. As shown in FIG. 9, theoperation control unit 7 has the I/F 71 that is an image input unit, theimage processing unit 73, and a modulation circuit 75 that is anexposure signal generating unit. The I/F 71 accepts image data suppliedfrom an external device such as a PC, or image data supplied through anetwork or the like. The image processing unit 73 performs prescribedimage processings regarding the character specification, outlinecorrection, tone correction, and γ characteristic and so on describedabove, to the image signal generated by the image reading unit 5 or theimage data from the I/F 71. The modulation circuit 75 converts the imagedata processed by the image processing unit 73 into a modulation signal(exposure signal) for laser light by the exposure unit 31.

The operation control unit 7 has a CPU (Central Processing Unit) 77, andan MPU (Main Processing Unit) 79. The CPU 77 controls an image signalsystem such as the I/F 71, the image processing unit 73, and themodulation circuit 75. The MPU 79 connects to the CPU 77, and controlsan operation of the whole MFP 1 including the image forming unit 3 andthe image reading unit 5. For example, the MPU 79 controls an imagereading operation of the image reading unit 5, an image formingoperation of the image forming unit 3, and a heating temperature of thefixing unit 35 at the time of an image erasing operation and an imagediscoloring operation described later.

The heating temperature of the fixing unit 35 is controlled by the MPU79 so as to be changed from a fixing temperature to an erasingtemperature at the time of image erasing operation, as described later.The heating temperature of the fixing unit 35 is controlled by the MPU79 so as to be changed from the fixing temperature to a discoloringtemperature at the time of image discoloring operation. The heatingtemperature of the fixing unit 35 is controlled by the MPU 79 so as tobe changed from the erasing temperature or the discoloring temperatureto the fixing temperature at the time of image forming operation.

The MPU 79 controls the respective units of the MFP 1 according to acontrol input from the operation panel 9 which accepts a userinstruction for the MFP 1. The operation panel 9 has a plurality of keysand the display panel 9 a. The plurality of keys of the operation panel9 include a start key which accepts a start instruction by a userrelating operations, such as image forming, image erasing, and imagediscoloring.

The display panel 9 a displays the states of the respective units of theMFP 1, such as a waiting time for changing the heating temperature ofthe fixing unit 35 at the time of image erasing, image discoloring, andfixing for image forming, and so on, by a user interface widely known asa character string or a sign (pictogram/icon). The display panel 9 aaccepts the control input by the user, and displays the contents of theaccepted input. The display panel 9 a displays the above-describedvarious contents according to the control of the MPU 79. The MPUconnects to an I/F (Interface) 72 for inputting and outputtinginformation between the MPU 79 and the operation panel 9.

The operation control unit 7 has a ROM (Read Only Memory) 111 thatstores a program, a RAM (Random Access Memory) 113, an NVM (Non-volatileMemory) 115, a page memory 117 and an I/O port (Input/Output Port) 119.The page memory 117 is a work memory to provide a work area of an imageprocessing in the image processing unit 73. The MPU 79 connects to theROM 111, the RAM 113, and the I/O port 119. The I/O port 119 inputs theoutput of a sensor 120 to the MPU 79.

The sensor 120 includes an ADU sensor to detect opening and closing ofthe ADU 40, and a tray sensor to detect a usable state of any one of themanual feed tray 46 and the second manual feed tray 146. The usablestate of any one of the manual feed tray 46 and the second manual feedtray 146 is a state indicating on which one of the fulcrum 46 a and thefulcrum 146 a, the manual feed tray 46 or the second manual feed tray146 is mounted. The sensor 120 further includes a temperature sensor todetect a heating temperature of the fixing unit 35, a sheet sensor todetect presence or absence of a sheet in the manual feed trays 46, 146,and a discharge sensor to detect that the sheet passes through thefixing unit 35, for example. The MPU 79 connects to a sensor S1. Thesensor S1 reads out a test pattern formed on the intermediate transferbelt 33 for image stabilization processing.

The MPU 79 connects to a motor driver 121 to control rotation ofarbitrary motors 131, 133, 139 and so on. The motor 131 drives the imageforming stations 321 a to 322 d and the intermediate transfer belt 33and so on, for example. The motor 133 drives the sheet conveying unitsfrom the cassette to the fixing unit 35 and the ADU 40, such as thesheet feeding mechanism 42, the separation mechanism 43, the conveyingmechanism 44, the aligning mechanism 45, and the secondary transfer unit34. Furthermore, the motor 133 drives the sheet conveying units from themanual feed tray 46 to the fixing unit 35, such as the sheet feedingmechanism 47, the separation mechanism 48, and the timing matchingmechanism 49. The motor 133 further drives the sheet conveying unitsfrom the second manual feed tray 146 to the fixing unit 35, such as thesheet feeding mechanism 147, the separation mechanism 148, and thesecond timing matching mechanism 149, and so on.

The motor 139 drives the fixing unit 35 independently from theabove-described conveying units 42-45, 47-49, 147-149. The motor 133drives any one conveying units of the conveying units 47-49 and theconveying units 147-149, and stops driving of the other conveying units,according to an output (detection result) of the tray sensor of thesensor 20. It is possible to drive the conveying units 47-49 and theconveying units 147-149 by independent motors.

The MPU 79 connects to a heater control device 123 to drive a heater 35a for changing the heating temperature of the fixing unit 35. The heatercontrol device 123 is a temperature control unit to control the heatingtemperature of the fixing unit 35 to a standby temperature, the fixingtemperature, the discoloring temperature, and the erasing temperature,described later. Specifically, the heater control device 123 controlsheating of the heater that is a heat source of the fixing unit 35. Aswill be described later, the heating temperature of the fixing unit 35can be changed by the heater 35 a, and thus the fixing unit 35 operatesfor fixing the image formed on the sheet, erasing the image, anddiscoloring the image.

An image erasing operation of the MFP 1 will be described with referenceto FIG. 10. FIG. 10 is a flowchart showing an image erasing operation ofthe MFP 1.

The discolorable toner which is used in the image (toner image) of thesheet decolors when heated at the erasing temperature, as describedabove. Specifically, in the discolorable toner, the action of the colordeveloper to the coloring compound (precursor compound of coloringmatter) is broken, and the coloring state is resolved, and thus thediscolorable toner decolors. The discolorable toner decolors, to causethe image of the sheet to be erased. In addition, when heated at thediscoloring temperature, the discolorable toner which is used in theimage of the sheet discolors from the original color to a transparentcolor, for example. The discolorable toner discolors, to cause the imageof the sheet to be discolored.

The fixing unit 35 has a roller incorporating the heater 35 a. Theheater 35 a is a heater lamp, for example. The fixing unit 35 may be aconfiguration having an IH (Induction Heating Coil) heater to causeinduction heat on a metal face of the roller, as the heater 35 a. Thefixing unit 35 may have a belt in place of the roller, and may be aconfiguration having an IH (Induction Heating Coil) heater to causeinduction heat on a metal layer of the belt, as the heater 35 a.

The fixing unit 35 heats the image on the sheet by the heater 35 a. Thefixing unit 35 can change the heating temperature by the heater 35 a tothe fixing temperature, the discoloring temperature higher than thefixing temperature, and the erasing temperature. When the heatingtemperature of the fixing unit 35 is the fixing temperature, the fixingunit 35 fixes the image of the sheet, as described above. When theheating temperature of the fixing unit 35 is the above-described erasingtemperature, the fixing unit 35 heats the image of the sheet at theerasing temperature, to decolor the toner and thereby erase the image ofthe sheet. When the heating temperature of the fixing unit 35 is theabove-described discoloring temperature, the fixing unit 35 heats theimage of the sheet at the discoloring temperature, to discolor the tonerto a transparent color, for example, and thereby discolor the image ofthe sheet. Without independently having a unit for erasing the image anddiscoloring the image, the MFP 1 can erase the image of the sheet anddiscolor the image by the fixing unit 35.

When the MFP 1 performs an operation to erase the image of the sheet, ifthe operation panel 9 accepts selection of the image erasing operationby a user, in an ACT 1 as shown in FIG. 10, the operation control unit 7makes the display panel 9 a display a message such as “Please open ADU”or the like.

In an ACT 2, the operation control unit 7 instructs the heater drivingdevice 123 to control the heater 35 a. The heater driving device 123starts a first temperature control of the heater 35 a so as to raise theheating temperature of the fixing unit 35 to the above-described erasingtemperature, according to the instruction from the operation controlunit 7.

In ACT 3, the control unit 7 judges whether or not the ADU 40 is opened,based on the detection result of the Above-described ADU sensor which isinputted to the operation control unit 7 through the I/O port 119. Whenthe operation control unit 7 judges that the ADU 40 is opened as shownin FIG. 8, the operation control unit 7 makes the display panel 9 adisplay a message for prompting the user to prepare the image erasingoperation, such as “Please load manual feed tray into ADU” or the like.

In an ACT 4, the operation control unit 7 judges whether or not themanual feed tray 46 or the second manual feed tray 146 is loaded on thefulcrum 146 a, based on the detection result of the above-described traysensor which is inputted through the I/O port 119. Hereinafter, thedescription will be made assuming that the manual feed tray 46 is loadedon the fulcrum 146 a. When the operation control unit 7 judges that themanual feed tray 46 is loaded on the rotation fulcrum 146 a as shown inFIG. 8, the operation of the MFP 1 proceeds to an ACT 5.

In the ACT 5, the operation control unit 7 judges whether or not theheating temperature of the fixing unit 35 reaches the above-describederasing temperature, based on the detection result of theabove-described temperature sensor which is inputted through the I/Oport 119. Furthermore, in the above-described ACT 5, the operationcontrol unit 7 judges whether or not there is a sheet in the manual feedtray 46 loaded on the fulcrum 146 a, based on the detection result ofthe above-described sheet sensor which is inputted through the I/O port119. When the operation control unit 7 judges that there is no sheet inthe manual feed tray 46, the operation control unit 7 makes the displaypanel 9 a display a message for prompting preparation of the imageerasing operation, such as “Please place sheet on manual feed tray” orthe like. When the operation control unit 7 judges that the heatingtemperature of the fixing unit 35 reaches the above-described erasingtemperature, and there is a sheet in the manual feed tray 46 (YES in ACT5), the operation of the MFP 1 proceeds to an ACT 6.

In the ACT 6, the operation control unit 7 makes the display panel 9 adisplay a message for prompting start of the image erasing operation,such as “Please turn ON start key” or the like. In the above-describedACT 6, when the operation control unit 7 judges that the operation panel9 accepts that the start key is turned ON, the operation of the MFP 1proceeds to an ACT 7.

In the ACT 7, the operation control unit 7 instructs the motor driver121 to control driving of the motor 133 and the motor 139. The motordriver 121 controls the motor 133 so that the above-described conveyingunits 147-149 are driven. The motor 133 drives the conveying units147-149. The conveying units 147-149 convey the sheet from the manualfeed tray 46 loaded on the fulcrum 146 a to the fixing unit 35. Themotor driver 121 controls the motor 139 so that the above-described thefixing unit 35 is driven.

The motor 139 drives the fixing unit 35. The fixing unit 35 erases theimage of the sheet while conveying the sheet. In the above-described ACT7, the operation control unit 7 judges whether or not the sheet haspassed through the fixing unit 35, in other words, the erasing of theimage of one sheet has been completed, based on the detection result ofthe above-described discharge sensor which is inputted through the I/Oport 119. When the operation control unit 7 judges that the erasing ofthe image of the one sheet has been completed, the operation of the MFP1 proceeds to an ACT 8.

In the ACT 8, the operation control unit 7 judges whether or not thereis a sheet in the manual feed tray 46 loaded on the fulcrum 146 a, basedon the detection result of the above-described sheet sensor which isinputted through the I/O port 119. When the operation control unit 7judges that there is a sheet in the manual feed tray 46 (YES in ACT 8),the operation of the MFP 1 returns to the ACT 7. When the operationcontrol unit 7 judges that there is no sheet in the manual feed tray 46(NO in ACT 8), the image erasing operation of the MFP 1 ends, and theMFP 1 becomes in a standby state.

Since the ADU 40 is in the open state during the image erasing operationof the above-described ACT 7, the motor driver 121 controls the motor133 and the motor 139 so that only the fixing unit 35 and the conveyingunits 147-149 are driven. Accordingly, since power consumed by the motor131 or the like to drive the image forming stations 321 a-322 d becomesunnecessary, it is possible to save power consumption of the MFP 1. TheMFP 1 can perform the image discoloring operation, as described above.The image discoloring operation is the same as the image erasingoperation which has been described with reference to FIG. 10, exceptthat the heating temperature of the fixing unit 35 is changed to thediscoloring temperature in place of the erasing temperature.Accordingly, the description of the image discoloring operation will beomitted.

An operation of the MFP 1 returning from the above-described imageerasing operation to the image forming operation will be described withreference to FIG. 11. FIG. 11 is a flowchart for describing thereturning operation from the image erasing operation to the imageforming operation in the MFP 1.

In the image erasing operation of FIG. 10, in order to erase the imageof the sheet, the heating temperature of the fixing unit 35 is changedto the above-described erasing temperature higher than theabove-described fixing temperature. Accordingly, when the image formingoperation is instructed by a user, a temperature control is necessary tolower the heating temperature of the fixing unit 35 from the erasingtemperature to the fixing temperature.

As shown in FIG. 11, in an ACT 11, when the operation panel 9 acceptstermination of the image erasing operation, such as selection of theimage forming operation, by the user, the operation control unit 7 makesthe display panel 9 a of the operation panel 9 display a message, suchas “Please unload manual feed tray from ADU, and close ADU” or the like.

In an ACT 12, the operation control unit 7 instructs the heater drivingdevice 123 to control the heater 35 a. The heater driving device 123starts a second temperature control of the heater 35 a so as to lowerthe heating temperature of the fixing unit 35 to the fixing temperature,according to the instruction from the operation control unit 7.

In an ACT 13, the operation control unit 7 judges whether or not theheating temperature of the fixing unit 35 reaches the above-describedfixing temperature, based on the detection result of the above-describedtemperature sensor which is inputted through the I/O port 119.

Specifically, the operation control unit 7 predicts whether or not atime required for the heating temperature of the fixing unit 35 to reachthe above-described fixing temperature is longer than a prescribed time,for example. In the above-described ACT 13, when the operation controlunit 7 predicts that the time required for the heating temperature ofthe fixing unit 35 to reach the above-described fixing temperature islonger than the prescribed time. (NO in the above-described ACT 13), theoperation of the MFP 1 proceeds to an ACT 14.

In the ACT 14, the operation control unit 7 instructs the motor driver121 to control driving of the motor 139. The motor driver 121 controlsonly the motor 139. The motor 139 operates for a prescribed time, todrive the fixing unit 35. The fixing unit 35 is driven, and thereby thedecrease of the heating temperature of the fixing unit 35 is promoted.The case in which the operation control unit 7 predicts that the timerequired for the heating temperature of the fixing unit 35 to reach theabove-described fixing temperature is longer than the prescribed time isa case in which the heating temperature of the fixing unit 35 is higherthan the fixing temperature, and the difference between the heatingtemperature and the fixing temperature is not less than 10% of thefixing temperature, for example.

In an ACT 15, after the fixing unit 35 has been driven for theabove-described prescribed time, the operation control unit 7 judgeswhether or not the heating temperature of the fixing unit 35 reaches theabove-described fixing temperature, based on the detection result of theabove-described temperature sensor which is inputted through the I/Oport 119 again. Specifically, as described above, the operation controlunit 7 predicts whether or not the time required for the heatingtemperature of the fixing unit 35 to reach the above-described fixingtemperature is longer than the above-described prescribed time.

In the above-described ACT 15, when the operation control unit 7predicts that the time required for the heating temperature of thefixing unit 35 to reach the above-described fixing temperature is longerthan the prescribed time (NO in the above-described ACT 15), theoperation of the MFP 1 returns to the above-described ACT 14. In theabove-described ACT 14, the motor driver 121 controls only the motor139, as described above. The motor 139 drives the fixing unit 35.

In the above-described ACT 13, when the operation control unit 7predicts that the time required for the heating temperature of thefixing unit 35 to reach the fixing temperature is within the range ofthe above-described prescribed time (YES in the above-described ACT 13),the operation of the MFP 1 proceeds to an ACT 16. Furthermore, in theabove-described ACT 15, when the operation control unit 7 predicts thatthe time required for the heating temperature of the fixing unit 35 toreach the fixing temperature is within the range of the prescribed time(YES in the above-described ACT 15), the operation of the MFP 1 proceedsto the ACT 16. The case in which the operation control unit 7 predictsthat the time required for the heating temperature of the fixing unit 35to reach the fixing temperature is within the range of the prescribedtime is a case in which the heating temperature of the fixing unit 35 ishigher than the fixing temperature, but the difference between theheating temperature and the fixing temperature is less than 10% of thefixing temperature, for example.

In the ACT 16, the operation control unit 7 makes the display panel 9 aof the operation panel 9 display a message for prompting the imageforming operation of the user, such as “Ready to copy” or the like.After the message for prompting the image forming operation of the useris displayed, a little time lag may occur until actually the temperatureof the fixing unit 35 completely becomes the fixing temperature.However, the time lag is not to such an extent that the user is aware ofan undesired waiting time. For example, in consideration of theoccurrence of the above-described time lag, the display panel 9 a maydisplay a message such as “Please wait for about 10 seconds” or thelike. The returning operation from the image discoloring operation tothe image forming operation is the same as the returning operation fromthe image erasing operation to the image forming operation which hasbeen described with reference to FIG. 11. Accordingly, the descriptionof the returning operation from the image discoloring operation to theimage forming operation will be omitted.

Hereinafter, switching of the image forming by a print mode will bedescribed.

The MFP 1 shown in FIG. 1, FIG. 2, and FIG. 7-FIG. 9 can form an imageby a print mode using discolorable toner or a print mode usingnon-discolorable toner. For example, a user operates the operation panel9, and thus can select any print mode out of a first print mode usingdiscolorable toner and a second print mode using non-discolorable toner.Specifically, the user can select the above-described print modes from amode selection screen of the display unit 9 a of the operation panel 9.When the operation panel 9 accepts selection of the above-describedfirst print mode, the operation control unit 7 selects the image formingby the first print mode. When the operation panel 9 accepts selection ofthe above-described second print mode, the operation control unit 7selects the image forming by the second print mode.

The operation control unit 7 controls execution of the image forming bythe image forming station 321 a at the position facing the housing unitto house the toner 51 a, in response to selection of the first printmode using discolorable toner by a user. The image forming station 321 ais controlled by the operation control unit 7, to form an image usingthe toner 51 a. Or, the operation control unit 7 controls execution ofthe image forming by the first to fourth image forming stations 321a-321 d at the positions facing the housing units to house the toners 51a-51 d, respectively, in response to selection of the first print modeusing discolorable toners by a user. The first to fourth image formingstations 321 a-321 d are controlled by the operation control unit 7, toform images using the toners 51 a-51 d, respectively.

The operation control unit 7 controls execution of the image forming bythe image forming station 322 a at the position facing the housing unitto house the toner 61 a, in response to selection of the second printmode using non-discolorable toner by a user. The image forming station322 a is controlled by the operation control unit 7, to form an imageusing the toner 61 a. Or, the operation control unit 7, controlsexecution of the image forming by the fifth to eighth image formingstations 322 a-322 d at the positions facing the housing units to housethe toners 61 a-61 d, respectively, in response to selection of thesecond print mode using non-discolorable toners by a user. The fifth toeighth image forming stations 322 a-322 d are controlled by theoperation control unit 7, to form images using the toners 61 a-61 d,respectively.

FIG. 3 is a diagram showing an example of a heating temperature of thefixing unit. For example, as shown in FIG. 3, the fixable temperature ofthe discolorable toner is about 150 degrees. The fixable temperature isa lower limit temperature of the fixing temperature at which a tonerimage is fixed to a sheet. The fixing temperature has a range from thelower limit temperature to an upper limit temperature lower than aspecified temperature. The specified temperature is a predeterminedtemperature. The fixable temperature of the non-discolorable toner isabout 170 degrees. The erasing temperature of the discolorable toner isabout 190 degrees higher than the above-described specified temperature.In the present embodiments, the case will be described in which thefixable temperature of the discolorable toner and the fixabletemperature of the non-discolorable toner are different, but the fixabletemperature of the discolorable toner and the fixable temperature of thenon-discolorable toner may be equal to each other.

When the first print mode to use the discolorable toner is selected by auser, or image forming by the first print mode to use the discolorabletoner is performed, the heater control device 123 performs ON/OFFcontrol of the heater 35 a, to control the heating temperature of thefixing unit 35 to a fixing temperature within the range from a firsttemperature to a second temperature. In addition, when the second printmode to use the non-discolorable toner is selected by a user, or imageforming by the second print mode to use the non-discolorable toner isperformed, the heater control device 123 performs ON/OFF control of theheater 35 a, to control the heating temperature of the fixing unit 35 toa fixing temperature within the range from a first temperature to asecond temperature.

For example, the heater control device 123 controls the heatingtemperature of the fixing unit 35 to the fixing temperature of the rangefrom the above-described 150 degrees to 180 degrees, for example. Theheater control device 123 detects temperatures in the vicinity of theheater and in the vicinity of the fixing unit 35, and controls theheating temperature of the fixing unit 35 to the fixing temperaturewithin the range from the above-described 150 degrees to 180 degrees,based on the temperature detection result. At the time of image erasingoperation, the heater control device 123 detects temperatures in thevicinity of the heater 35 a and in the vicinity of the fixing unit 35,and controls the heating temperature of the fixing unit 35 to theerasing temperature within the range from the above-described 190degrees to 195 degrees, for example, based on the temperature detectionresult.

While the MFP 1 continuously forms images by the above-described printmode, the MFP 1 may be unable to keep the heating temperature of thefixing unit 35 to the fixing temperature sometimes. In some cases, whilethe MFP 1 performs image forming by the first print mode using thediscolorable toner, the heating temperature of the fixing unit 35 mayexceed 180 degrees that is the upper limit temperature of the fixingtemperature, or exceed 185 degrees, or exceed 190 degrees. If theheating temperature of the fixing unit 35 does not reach the erasingtemperature, but has exceeded the fixing temperature, the image formedusing the discolorable toner may discolor and deteriorate, at the timeof fixing the image by the fixing unit 35. In addition, if the heatingtemperature of the fixing unit 35 has reached the erasing temperature,or has exceeded the erasing temperature, the image formed with thediscolorable toner is erased, at the time of fixing the image by thefixing unit 35.

FIG. 4 is a view showing switching of the print mode. As shown in FIG.4, While the image forming by the first print mode using thediscolorable toner is selected, or while the image forming is executedby the first print mode, in case that the heating temperature of thefixing unit 35 has exceeded the fixing temperature, in case that theheating temperature of the fixing unit 35 has reached the erasingtemperature of the discolorable toner, or in case that the heatingtemperature has exceeded the erasing temperature, the MPU 79 of theoperation control unit 7 turns OFF the heater 35 a that is the heatsource of the fixing unit 35, to interrupt the image forming with thediscolorable toner. The MPU 79 selects the image forming by the secondprint mode using the non-discolorable toner. In other words, the MPU 79switches the image forming of the MFP 1 from the image forming by thefirst print mode to the image forming by the second print mode. The MFP1 does not resume the image forming by the first print mode until theheating temperature of the fixing unit 35 falls within the range of thefixing temperature of the discolorable toner.

The MPU 79 of the operation control unit 7 controls output ofinformation relating to interruption of the image forming by the firstprint mode, and information relating to selection of the image formingby the second print mode. In other words, the MPU 79 controls output ofinformation relating to interruption of the image forming using thediscolorable toner, and information relating to switching from the imageforming using the discolorable toner to the image forming with thenon-discolorable toner. The display unit 9 a displays the informationrelating to the interruption of the image forming by the first printmode, and the selection of the image forming by the second print mode,in accordance with the output of the above-described information. Inother words, the display unit 9 a displays the information relating tothe interruption of the image forming using the discolorable toner, andthe information relating to the switching from the image forming usingthe discolorable toner to the image forming using the non-discolorabletoner. FIG. 5A and FIG. 5B are views each showing a display screen 91which the display unit 9 a displays. The display screen 91 has a guidedisplay area 92. As shown in FIG. 5A, the display unit 9 a displays amessage of “switched from printing using discolorable toner to printingusing non-discolorable toner”, for example, in the guide display area92. Furthermore, the image forming unit 3 may form informationindicating the image forming with the non-discolorable toner, such as amark, on a sheet, along with an image that is an object to be printed. Auser visually observes the above-described mark of the image printedsheet, to recognize that the present image forming is the image formingwith the non-discolorable toner.

When the heating temperature of the fixing unit 35 falls within therange of the fixing temperature, the MPU 79 of the operation controlunit 7 controls the image forming by the image forming unit 3, so thatthe MFP 1 resumes the image forming by the first print mode using thediscolorable toner. In other words, the MPU 79 switches the imageforming of the MFP 1 from the image forming by the second print modeusing the non-discolorable toner to the image forming by the first printmode using the discolorable toner.

The MPU 79 of the operation control unit 7 controls output ofinformation relating to switching from the image forming by the secondprint mode to the image forming by the first print mode. In other words,the MPU 79 controls output of information relating to the switching fromthe image forming using the non-discolorable toner to the image formingwith the discolorable toner. The display unit 9 a displays a message of“returned to printing using discolorable toner”, for example, in theguide display area 92, as shown in FIG. 5B. Furthermore, the imageforming unit 3 may form information indicating the image forming withthe discolorable toner, such as a mark, on a sheet, along with an imagethat is an object to be printed. A user visually observes theabove-described mark of the image printed sheet, to recognize that thepresent image forming is the image forming with the discolorable toner.

A user operates the display unit 9 a of the operation panel 9, andthereby can designate validity or invalidity of the execution ofautomatic switching to the above-described second print mode. When theoperation panel accepts the designation by the user that the executionof the above-described automatic switching is valid, the MPU 79 of theoperation control unit 7 sets the execution of the above-describedautomatic switching to be valid. When the operation panel accepts thedesignation by the user that the execution of the above-describedautomatic switching is invalid, the MPU 79 sets the execution of theabove-described automatic switching to be invalid. In accordance withthe setting that the execution of the above-described automaticswitching is valid, when the heating temperature of the fixing unit 35has exceeded the fixing temperature, when the heating temperature of thefixing unit 35 has reached the erasing temperature of the discolorabletoner, or when the heating temperature of the fixing unit 35 hasexceeded the erasing temperature, the MPU 79 interrupts the imageforming by the first print mode, and automatically switches the imageforming of the MFP 1 from the image forming by the first print mode tothe image forming by the second print mode.

In accordance with the setting that the execution of the above-describedautomatic switching is invalid, when the heating temperature of thefixing unit 35 has exceeded the fixing temperature, when the heatingtemperature of the fixing unit 35 has reached the erasing temperature ofthe discolorable toner, or when the heating temperature of the fixingunit 35 has exceeded the erasing temperature, the MPU 79 interrupts theimage forming by the first print mode. When the execution of theabove-described automatic switching is set to be invalid, the MPU 79does not execute automatic switching from the image forming by the firstprint mode to the image forming by the second print mode.

As described above, even in case that the heating temperature of thefixing unit 35 has become a high temperature, the image forming by thesecond print mode using the non-discolorable toner is executed, andthereby the MFP 1 can effectively use the time till the heatingtemperature of the fixing unit 35 falls within the fixing temperature.

An example of execution control of the switching of the image forming bythe above-described print mode will be described with reference to FIG.6. FIG. 6 is a flowchart showing an example of execution control of theswitching of the image forming by the above-described print mode.

For example, when the MFP 1 is started, the heater control device 123starts heating by the heater 35 a that is the heating source of thefixing unit 35. After the heating is started, the heater control device123 performs ON/OFF control of the heating by the heater 35 a. Theheating temperature of the fixing unit 35 is maintained to the standbytemperature that is a ready temperature, by the control of the heatercontrol device 123.

For example, when a user operates the display unit 9 a of the operationpanel 9, to instruct print start in the print mode using thediscolorable toner or the non-discolorable toner, the heater controldevice 123 performs ON/OFF control of the heating by the heater 35 a ofthe fixing unit 35 maintained to the standby temperature. The heatingtemperature of the fixing unit 35 is maintained to the fixingtemperature by the control of the heater control device 123. When theheating temperature of the fixing unit 35 reaches the fixabletemperature, the MFP 1 becomes able to print. The image forming unit 3starts printing.

Specifically, in an ACT 101 of FIG. 6, the display unit 9 a of theoperation panel 9 accepts selection by a user of the first print modeusing the discolorable toner. Furthermore, in an ACT 102, the operationpanel 9 accepts an instruction of print start by the user.

In an ACT 103, the operation control unit 7 judges whether or not theheating temperature of the fixing unit 35 is the fixing temperature,based on the temperature detection result of the sensor. In other words,the operation control unit 7 judges whether or not the heatingtemperature of the fixing unit 35 is maintained within the range of thefixing temperature lower than the erasing temperature. When theoperation control unit 7 judges that the heating temperature of thefixing unit 35 is maintained to the fixing temperature (YES in ACT 103),the operation of the MFP 1 proceeds to an ACT 104.

In the ACT 104, the operation control unit 7 controls the image formingby the image forming unit 3 so that the MFP 1 executes the image formingby the first print mode. The image forming unit 3 executes the imageforming by the first print mode using the discolorable toner. In an ACT105, the MPU 79 of the operation control unit 7 controls the conveyingunits so as to discharge the image printed sheet to the first sheetdischarge tray T11. The conveying units discharge the image printedsheet to the first sheet discharge tray T11. In an ACT 106, the displayunit 9 a is controlled by the operation control unit 7, to display amessage such as “during printing with discolorable toner”.

In an ACT 112, the operation control unit 7 judges whether or not theimage forming for the sheets of a number previously set by a user isfinished, each time the image forming for a sheet is finished, forexample. When the operation control unit 7 judges that the image formingfor the sheets of the set number is not finished (NO in ACT 112), theoperation of the MFP 1 returns to the ACT 103.

The MFP 1 repeats the above-described processings from the ACT 103 tothe ACT 112, until the image forming for the sheets of the set number isfinished. When the operation control unit 7 judges that the imageforming for the sheets of the set number has been finished (YES in ACT112), the operation of the MFP 1 proceeds to an ACT 113. In the ACT 113,the operation control unit 7 finishes control for image forming by theimage forming unit 3. Accordingly, the MFP 1 finishes printing in thefirst print mode using the discolorable toner.

On the other hand, when the display unit 9 a accepts selection by a userof the first print mode using the discolorable toner (theabove-described ACT 101), the operation panel 9 accepts an instructionof print start by the user (the above-described ACT 102), and theoperation control unit 7 judges that the heating temperature of thefixing unit 35 exceeds the upper limit of the fixing temperature (NO inthe above-described ACT 103), the operation of the MFP 1 proceeds to anACT 107. That the heating temperature of the fixing unit exceeds theupper limit of the fixing temperature may be the case in which theheating temperature approaches the erasing temperature, for example, orthe case in which the heating temperature exceeds the erasingtemperature.

In the ACT 107, the MPU 79 of the operation control unit 7 controls theheater control device 123. The heater control device 123 turns OFFheating by the heater 35 a. The MPU 79 controls execution interruptionof the image forming by the image forming unit 3. The image forming unit3 is controlled by the MPU 79, to interrupt the image forming by thefirst print mode using the discolorable toner. The operation controlunit 7 judges whether the execution of the automatic switching of theimage forming by the print mode is set to be valid or set to be invalid.When the operation control unit 7 judges that the execution of theabove-described automatic switching is set to be invalid (NO in ACT107), the operation of the MFP 1 proceeds to an ACT 108.

In the ACT 108, the operation control unit 7 controls executioninterruption of the image forming by the image forming unit 3, till theheating temperature of the fixing unit 35 drops and falls within therange of the fixing temperature. In other words, the operation controlunit 7 controls so that the image forming by the image forming unit 3 isnot resumed, till the heating temperature of the fixing unit 35 dropsand falls within the range of the fixing temperature. The operation ofthe MFP 1 returns to the ACT 103 after a prescribed time elapses, forexample. In the above-described ACT 107, when the operation control unit7 judges that the execution of the above-described automatic switchingis set to be valid (YES in ACT 107), the operation of the MFP 1 proceedsto an ACT 109.

In the ACT 109, the MPU 79 of the operation control unit 7 switches theimage forming of the MFP 1, from the image forming by the first printmode to the image forming by the second print mode. The MPU 79 controlsthe image forming by the image forming unit 3 so that the MFP 1 executesthe image forming by the second print mode. The image forming unit 3executes the image forming by the second print mode using thenon-discolorable toner. In an ACT 110, the MPU 79 of the operationcontrol unit 7 controls the conveying units so as to discharge the imageprinted sheet to the second sheet discharge tray T12. The conveyingunits discharge the image printed sheet to the second sheet dischargetray T12.

In an ACT 111, the display unit 9 a is controlled by the operationcontrol unit 7, to display a message such as “during printing withnon-discolorable toner”. When the MFP 1 finishes the image forming bythe second print mode to one sheet, the operation of the MFP 1 returnsto the above-described ACT 112.

In the above-described description, the case has been described inwhich, when the heating temperature of the fixing unit 35 exceeds theupper limit temperature of the fixing temperature, approaches theerasing temperature, or exceeds the erasing temperature, the imageforming by the first print mode using the discolorable toner isinterrupted, and the image forming by the second print mode using thenon-discolorable toner is executed, but the present embodiment is notlimited to this. For example, the MFP 1 further has a high speed printmode using the discolorable toner, and a high image quality print modeusing the discolorable toner. When a user selects the Above-describedhigh speed print mode, even if the heating temperature of the fixingunit 35 exceeds the upper limit temperature of the fixable temperature,but if it does not approach the erasing temperature, that is, if it isnot more than 185 degrees, for example, the operation control unit 7controls the image forming by the image forming unit 3, so that the MFP1 executes the image forming by the high speed print mode.

The image forming unit 3 executes the image forming by the high speedprint mode using the discolorable toner. When a user selects theabove-described high image quality print mode, in case that the heatingtemperature of the fixing unit 35 exceeds the upper limit temperature ofthe fixing temperature, the operation control unit 7 controls executioninterruption of the image forming by the image forming unit 3. The imageforming unit 3 interrupts the execution of the image forming by the highimage quality print mode using the discolorable toner.

The fixing unit 35 fixes an image in the state in which the heatingtemperature of the fixing unit 35 exceeds the upper limit temperature ofthe fixing temperature, and approaches the erasing temperature, and thusthe MFP 1 can also realize light color printing. For example, the fixingunit 35 heats the image of the discolorable toner at about 185 degrees,the MFP 1 can also realize printing of a light color image.

According to the MFP 1 of the present embodiment, it is possible toimprove defects due to temperature rise of the fixing unit 35. Forexample, when the heating temperature of the fixing unit 35 exceeds theupper limit temperature of the fixing temperature, or approaches theerasing temperature, or exceeds the erasing temperature, the MFP 1interrupts the image forming using the discolorable toner. The imageforming is interrupted, and thus it can be prevented that an image withdeteriorated image quality, or an image which has been erased has beenformed, in the first print mode using the discolorable toner.

When the heating temperature of the fixing unit 35 exceeds the upperlimit temperature of the fixing temperature, or approaches the erasingtemperature, or exceeds the erasing temperature, the MFP 1 interruptsthe image forming with the discolorable toner, and further executes theimage forming using the non-discolorable toner, in place of the imageforming using the discolorable toner.

When the heating temperature of the fixing unit 35 exceeds the erasingtemperature, the MFP 1 may execute the erasing operation. For example,when a sheet on which an image has been formed with the discolorabletoner is held in the above-described manual feed tray 146, and theheating temperature of the fixing unit 35 exceeds the erasingtemperature, the MFP 1 executes the erasing operation. Specifically, theMFP 1 feeds and conveys the sheet which is held in the above-describedmanual feed tray 146 to the fixing unit 35, and heats the image printedon the sheet by the fixing unit 35, to erase the image.

The above-described coloring material, such as toner or ink, contains acoloring compound, a color developer and a binder resin and so on, asdescribed above. When the coloring material in the state in which thecoloring compound has generated a color upon receiving the action of thecolor developer is heated at a prescribed temperature, the binder resinsoftens, and mainly the color developer becomes easy to move from theinside of the binder resin to the surface, and moves and/or diffusesinto the sheet. Accordingly, the coloring compound becomes not toreceive the action of the color developer, and thus the color of thecoloring compound becomes not recognizable by a user.

The above-described coloring compound is a precursor compound of thecoloring matter to form an image. As the coloring compound, it ispreferable to use electron donating organic matter, such as,leuko-auramines, diarylphthalides, polyarylcarbinols, acylauramines,arylauramines, rhodamine B lactams, indolines, spiropyrans, fluorans,and so on.

The above-described color developer is a compound to make the coloringcompound generate a color by the mutual action (mainly giving andreceiving electrons or protons) with the coloring compound. As the colordeveloper, it is preferable to use phenols, phenol metal salts,carboxylic acid metal salts, benzophenones, sulfuric acid, sulfonates,phosphoric acids, phosphoric acid metal salts, acidic phosphate ester,acidic phosphate ester metal salts, phosphorous acids, phosphorous acidmetal salts, and so on.

The above-described binder resin is to disperse the coloring compoundand the color developer in the color developing state. The binder resinmay be one representing characteristics that the one becomes compatiblewith the coloring compound when prescribed heat is given, and does nothave affinity with the color developer

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An image forming apparatus, comprising: an imageforming unit configured to execute any image forming out of imageforming to form an image on a recording medium by a first mode using adiscolorable coloring material which discolors by heating, and imageforming to form an image on a recording medium by a second mode using anon-discolorable coloring material; a fixing unit configured to heat theimage formed on the recording medium at a fixing temperature lower thana heating temperature at which the discolorable coloring materialdiscolors, to fix the image on the recording medium; a temperaturecontrol unit configured to control a heating temperature of the fixingunit to the fixing temperature; and an operation control unit configuredto select the image forming by the second mode, when the heatingtemperature of the fixing unit becomes a temperature higher than thefixing temperature.
 2. The image forming apparatus according to claim 1,wherein: while the image forming by the first mode is selected, when theheating temperature of the fixing unit becomes the temperature higherthan the fixing temperature, the operation control unit selects theimage forming by the second mode.
 3. The image forming apparatusaccording to claim 2, wherein: while the image forming unit executes theimage forming by the first mode, when the heating temperature of thefixing unit becomes the temperature higher than the fixing temperature,the operation control unit switches the image forming by the first modeto the image forming by the second mode.
 4. The image forming apparatusaccording to claim 1, wherein: the fixing temperature is a temperaturelower than a specified temperature, the heating temperature at which thediscolorable coloring material discolors is a temperature higher thanthe specified temperature, and when the heating temperature of thefixing unit becomes the temperature higher than the specifiedtemperature, the operation control unit selects the image forming by thesecond mode.
 5. The image forming apparatus according to claim 1,wherein: the operation control unit further outputs information relatingto selection of the image forming by the second mode.
 6. The imageforming apparatus according to claim 3, wherein: the operation controlunit outputs information relating to switching from the image forming bythe first mode to the image forming by the second mode.
 7. The imageforming apparatus according to claim 3, wherein: after the operationcontrol unit switches the image forming from the image forming by thefirst mode to the image forming by the second mode, when the heatingtemperature of the fixing unit becomes the fixing temperature, theoperation control unit switches the image forming from the image formingby the second mode to the image forming by the first mode,
 8. The imageforming apparatus according to claim 3, further comprising an operationpanel to accept selection of any one mode out of the first mode and thesecond mode, wherein: when the operation panel accepts the first mode,the image forming unit selects the image forming by the first mode, andwhen the operation panel accepts the second mode, the image forming unitselects the image forming by the second mode, and while the operationcontrol unit selects the image forming by the first mode, when theheating temperature of the fixing unit becomes the temperature higherthan the fixing temperature, the operation control unit selects theimage forming by the second mode.
 9. The image forming apparatusaccording to claim 8, wherein: the operation panel accepts designationto validate or invalidate execution of switching from the image formingby the first mode to the image forming by the second mode, and theoperation control unit controls the execution of the switching to theimage forming by the second mode, in accordance with the acceptance ofthe designation by the operation panel.
 10. The image forming apparatusaccording to claim 1, wherein: the discolorable coloring material is acoloring material which discolors by heating.